Synthesis of C-xylopyranosyl- and xylopyranosylidene-spiro-heterocycles as potential inhibitors of glycogen phosphorylase.

New derivatives of d-xylose with aglycons of the most efficient glucose derived inhibitors of glycogen phosphorylase were synthesized to explore the specificity of the enzyme towards the structure of the sugar part of the molecules. Thus, 2-(β-d-xylopyranosyl)benzimidazole and 3-substituted-5-(β-d-xylopyranosyl)-1,2,4-triazoles were obtained in multistep procedures from O-perbenzoylated β-d-xylopyranosyl cyanide. Cycloadditions of nitrile-oxides and O-peracetylated exo-xylal obtained from the corresponding β-d-xylopyranosyl cyanide furnished xylopyranosylidene-spiro-isoxazoline derivatives. Oxidative ring closure of O-peracetylated β-d-xylopyranosyl-thiohydroximates prepared from 1-thio-β-d-xylopyranose and nitrile-oxides gave xylopyranosylidene-spiro-oxathiazoles. The fully deprotected test compounds were assayed against rabbit muscle glycogen phosphorylase b to show moderate inhibition for 3-(2-naphthyl)-5-(β-d-xylopyranosyl)-1,2,4-triazole (IC50=0.9mM) only.